1. Field of the Invention
The invention describes a new process for the material and thermal utilisation of residual materials containing water, minerals and combustible parts, especially from the paper industry, in cement kilns, for the production of Portland cement clinker.
2. Description of Related Art
In a series of industrial processes, sludges are produced in comparatively large amounts as waste which contain comparatively large amounts of water (30-70%), combustible organic substances (10-30%) and mineral filling materials, especially clay, silicate and lime (10-50%). Typical examples herefor is the waste sludge obtained in the recycling of waste paper or lacquers. Since a further processing of such products is, in most cases, not possible, it is necessary either to dump or burn them, whereby a high portion of ash is again obtained which must be dumped. The high portion of water is extremely disturbing for both processes so that, in the past, these residual materials had to be dried, often with high investment expense. However, the general shortage and expense of dumping possibilities and the dissipation of the residual minerals contained in the sludge wastes and the thermal energy contained in the organic components obliges one to look for a process to utilise such materials in another way.
By way of example, the production of paper is referred to. The clay-containing materials used in the case of paper production as filling material and for the surface coating remain behind in the working up of waste paper, together with fine-fibred cellulose, as residual material. This corresponds to the following average composition:
______________________________________ dry substance about 35-65% water about 65-35% mineral portion about 10-30% combustible portion about 10-35% calorific value about 3000-4000 kJ/kg. ______________________________________
A material and thermal utilisation of worthwhile amounts of such undried and untreated paper residual materials hitherto failed because of suitable processes and devices which make possible an economic and environmentally compatible utilisation. Therefore, the residual materials must be pre-dried, with high investment cost, to a residual water content of 10-30%.
Therefore, the task arises to find a process by means of which one can further work up residual materials containing water, mineral and combustible portions without previous drying and without the production of wastes to be dumped to give a usable end product.